The proposed project will investigate the function(s) of hepatic malic enzyme in rats in which the activity of the enzyme has been increased by treatment with a protein restricted diet. The possible involvement of the enzyme in carboxylation of pyruvate to malate and subsequent conversion to amino acids will be studied by utilizing perfused liver and isolated liver cell preparations. The separation and quantitative assay of key intermediates in the process of biosynthesis of nonessential amino acids from malate will be performed in order to evaluate the contribution of malic enzyme to the total synthesis of these amino acids. The regulatory mechanisms which control the steady state level of hepatic malic enzyme will be investigated employing combined immunological and tracer techniques, as well as inhibitors of protein synthesis and changes in dietary regime. The role of the cytosol and mitochondrial malic enzyme isozymes in the metabolism of heart and brain will also be studied and, in particular, the possible contribution of the isozymes to a shuttle mechanism for the transport of reducing equivalents between the subcellular compartments will be investigated. A study of other metabolic reactions, in particular fatty acid chain elongation, which may require the intramitochondrial generation of NADPH will also be part of the proposed research.